Displacement mapping: Difference between revisions

Revision as of 12:49, 27 August 2011

Revision as of 12:54, 27 August 2011

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[[Image:Displacement.jpg|thumb|Displacement mapping]]

'''Displacement mapping''' is an alternative computer graphics technique in contrast to [[bump mapping]], [[normal mapping]], and [[parallax mapping]], using a ([[procedural texture|procedural]]-) [[texture mapping|texture-]] or [[heightmap|height map]] to cause an effect where the actual geometric position of points over the textured surface are ''displaced'', often along the [[Locally|local]] [[surface normal]], according to the value the texture function evaluates to at each point on the surface. It gives surfaces a great sense of depth and detail, permitting in particular self-occlusion, [[self-shadowing]] and silhouettes; on the other hand, it is the most costly of this class of techniques owing to the large amount of additional geometry.

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Other renderers that require the modeling application to deliver objects pre-tessellated into arbitrary polygons or even triangles have defined the term displacement mapping as moving the vertices of these polygons. Often the displacement direction is also limited to the surface normal at the vertex. While conceptually similar, those polygons are usually a lot larger than micropolygons. The quality achieved from this approach is thus limited by the geometry's tessellation density a long time before the renderer gets access to it.

This difference between displacement mapping in micropolygon renderers vs. displacement mapping in a non-tessellating (macro)polygon renderers can often lead to confusion in conversations between people whose exposure to each technology or implementation is limited. Even more so, as in recent years, many non-micropolygon renderers have added the ability to do displacement mapping of a quality similar to what a micropolygon renderer is able to deliver, naturally. To distinguish between the crude pre-tessellation-based displacement these renderers did before, the term '''sub-pixel displacement''' was introduced to describe this feature.{{cnCitation needed|date=August 2011}}

Sub-pixel displacement commonly refers to finer re-tessellation of geometry that was already tessellated into polygons. This re-tessellation results in micropolygons or often microtriangles. The vertices of these then get moved along their normals to archive the displacement mapping.